1. Field of the Invention
This invention pertains to apparatus for delaying transmission of a pneumatic fluid. More particularly, this invention pertains to an apparatus for delaying a pneumatic actuation of a fire suppression system.
2. Description of the Prior Art
Fire suppression systems are used in a wide variety of applications. A common fire suppression system will include a fire suppressant and an actuator for activating delivery of the fire suppressant to a hazard site. For example, the fire suppressant may be contained within a pressurized container. The activation mechanism may include an activation head, which drives a valve coupled to the container for release of the fire suppressant upon actuation of the valve. The fire suppressant is delivered through tubing or the like to a nozzle, which is directed at a potential fire location. Fire suppression systems may be provided in buildings, transportation equipment such as vehicles, vessels or other installations where fire is a threat.
Not uncommonly, fire suppression systems may include automatic activation systems in the event of a detected fire. For example, buildings are commonly provided with automatic activation systems having a mechanical thermal sensor which degrades in response to heat. Such sensors may be a eutectic metal or thermal bulb technology, which degrades (such as melting or breaking) upon being exposed to a set temperature. In the event of such degradation of the element, the fire suppressant may be released through a nozzle.
Remote mechanical thermal detectors are known in the prior art. An example of a mechanical thermal detector utilizes a mechanical thermal sensor coupled to a control unit. The control unit may contain a source of a pressurized gas, which, upon detection of a fire by the mechanical thermal detector, releases the pressurized gas to an actuation head. The pressurized gas may be a small volume of pressurized nitrogen. The gas is released along a tubing to a pressure-activated actuation head coupled to the valve of a suppressant container. As an alternative to using a finite volume of a pressurized gas, the control unit may be connected to an unlimited source of a pressurized gas.
An example of a prior art system involving heat detectors, control units and pneumatic circuits for driving a pneumatically controlled actuator are described in “Kidde WHDR™ Wet Chemical Fire Suppression System, Addendum No. 6 to Installation, Operation and Maintenance Manual, Part No. 87-12200-001, UL EX 3559, Design and Installation Instructions for XV Control Systems”, dated September 2002 and published by the assignee of the present invention.
In fire suppression systems, it is known to be desirable to provide a time delay between release of a pressurized gas by a control unit and actuation of the actuation head for releasing suppressant from the suppressant container.
There are several reasons that a time delay may be desired in a fire suppression system application. For reasons of safety, it may be important to delay to the release of a fire suppressant to allow a service technician or other occupant time to exit or perform some pertinent shutdown function. For example, once a fire is detected, it is common to a have a control system send a signal to operate a siren, horn or strobe light indicating a discharge of a fire suppressant is imminent. A time delay permits occupant egress or other preparations. Also, in the case of certain applications such as fire suppressant for spray booths or the like, a delay in the release of a fire suppressant permits an exhaust fan wind-down. In this example, it is important to delay the discharge of a dry chemical fire suppressant until the exhaust fans are stopped to maximize the effective discharge of the dry chemical.
FIG. 1 illustrates a prior art apparatus 10′ which includes a fire suppressant container 12′ and a pneumatically activated actuation head 14′. A remote thermal detector 20′ is coupled to a control unit 30′ by a cable 22′. A source 40′ of pressurized gas (such as nitrogen) is connected to the controller 30′ by a pneumatic conduit 42′. A pneumatic conduit 44′ connects the control unit 30′ to a time delay apparatus TDA. An outlet of the time delay apparatus TDA is connected by a pneumatic conduit 51′ to the actuation head 14′. The actuation head 14′ drives a valve (not shown) for release of suppressant from the container 12′. The suppressant flows through a tubing 15′ to an outlet nozzle 16′ located in the vicinity of a fire threat.
A prior art time delay apparatus TDA is illustrated in FIGS. 2 and 3 and is designated by numeral 50′. The prior art apparatus 50′ includes a housing 52′ formed of stock metal or the like which is machined or cast to form the various cavities and pathways that will be described herein. The housing 50′ includes an upper end 52a′ and a lower end 52b′. 
At the upper end 52a′, a threaded bore 63′ is machined into the housing 52′ with an axis Y′-Y′ (FIG. 2) centrally positioned and extending between the ends 52a′, 52b′. A hollow end cap 70′ having external threads (schematically shown at 71′) is threadedly received within the bore 63′. The interior of the end cap 70′ defines an accumulation chamber 68′. An O-ring 65′ seals the accumulation chamber 68′ against the housing 52′.
An elongated chamber 54′ is formed in the housing 50′ with its axis X′-X′ parallel to and offset from axis Y′-Y′. In the sectional view of FIG. 3, axis Y′-Y′ is behind axis X′-X′ and, therefore, not visible. An upper end 54a′ of the chamber 54′ communicates with the accumulation chamber 68′. A reduced diameter lower end 54b′ extends through the housing lower end 52b′. 
A spool 57′ is positioned within the chamber 54′ for movement along axis X′-X′. The spool 57′ is machined in close tolerance to the chamber 54′ except for a reduced diameter portion 76′. Opposing surfaces of the reduced diameter portion 76′ and the chamber 54′ define an annular chamber 76a′ sealed by upper and lower O-rings 74′, 62′. A reduced diameter pin 55′ extends from the lower end of the spool 57′ through the lower opening 54b′. The spool 57′ moves along axis X′-X′ from a blocking position (shown in FIG. 3) to an open position by movement of the spool 57′ toward lower end 52b′ and against the bias of a spring 60′ surrounding pin 55′.
With reference to FIG. 3, the housing 52′ has an inlet port 56′ adapted to be connected to the pneumatic conduit 44′ of FIG. 1. The housing 52′ further includes an outlet port 58′ for connection to the outlet pneumatic conduit 51′ of FIG. 1.
The ports 56′ and 58′ are connected by a primary pneumatic path including a portion 56a′ extending from inlet port 56′ and a portion 58a′ extending from outlet port 58′. Both the portions 56a′ and 58a′ communicate with the chamber 54′ but are axially offset from one another as illustrated in FIG. 3.
When in the closed position of FIG. 3, the spool 57′ is opposing the first pneumatic path portion 56a′ with path portion 56a′ is positioned between O-rings 62′ and 64′. As a result, pressurized fluid within the first pneumatic path portion 56a′ cannot urge the spool 57′ to move against the bias of the spring 60′. In the open position, the spool 57′ is moved against the bias of spring 60′ (as will be described) to a position with both of the pneumatic path portions 56a′, 58a′ in communication with the annular chamber 76a′. 
A secondary flow path 66′ extends from the first pneumatic portion 56a′ to the accumulation chamber 68′. A filter 72′ (FIG. 3) associated with the secondary flow path 66′ to impede the flow of gas into the accumulation chamber 68′.
The filter 72′ is formed of sintered metal or sintered ceramic material. The porous nature of the filter 72′ delays the flow of pressurized gas filling the accumulation chamber 68′ thereby delaying the build-up of pressure against the upper O-ring 74′. After the occurrence of such delay, the pressure within the accumulation chamber 68′ is sufficient to act against the O-ring 74′ to urge the spool 57′ against the bias of the spring 60′ to the open position. In the open position, the annular chamber 76a′ connects the first and second portions 56a′, 58a′ to open the primary pneumatic path between ports 56′, 58′. This permits the flow of pressurized gas to the actuation head 14′.
As is known in the prior art, the amount of delay imparted by the delay apparatus 50′ varies with the selection of the filter 72′. In a fire suppression system, a desired amount of delay may vary between ten to twenty seconds or more depending upon the particular application for use of the system 10′.
The design of the prior art mechanical delay 50′ may also be varied to add additional delay by reason of adding an enlarged accumulation chamber cavity to add an additional time delay. Such a cavity 68a′ is shown in FIG. 2 in fluid flow communication with the chamber 68′ thereby increasing the volume of the accumulation chamber.
The volume of the chamber 68′ may be determined at the time of the design of a particular delay apparatus to add or reduce the amount of delay by a desired amount. Further, the amount of delay can be varied by selecting the porosity of the filter. However, once the design of the filter has been selected and once the volume of chambers 68′, 68a′ has been selected, there is little opportunity to vary the time delay of a particular prior art apparatus 10′.
While prior art delay apparatus 10′ is useful for adding a delay to a pneumatic system, certain features of such designs result in a lack of precise control of the amount of delay to be provided by a prior art apparatus 10′. For example, manufacturing tolerances of the sintered filter 72′, the spring 60′ as well as the dimensions for all internal chambers and pathways, O-rings and other components can result in variability of the individual actual delay times of manufactured prior art apparatus even though they are designed to have identical delay times. Also, an adjustable time delay results in a single design being suitable for a wider range of desired time delay applications.
It is an object of the present invention to provide a design permitting a more consistent and reliable delay time and which permits adjustment of a time delay.